There is software for controlling an inverter, which includes a method of determining a motor constant by conducting a winding resistance measurement, a lock test and a no-load test, as shown in JEC-37 (Prior Art Example 1). Also, JP-A-7-55899 discloses a method of tuning a constant of an induction motor while the induction motor remains inoperative (Prior Art Example 2). In this method, a single-phase AC current is supplied to an induction motor, and a detected d-axis current value or a detected q-axis current value is expanded in Fourier series to determine a constant of the induction motor. Here, d-q axis coordinates are rotating coordinates which rotate at the same velocity as a rotating magnetic field of the motor.
The method shown in Prior Art Example 1 is not suitable for automatic measurements by means of driving an inverter because it involves operations for fixing a rotor of an induction motor and releasing the fixation between a lock test and a no-load current test.
Also, in the no-load current test, the induction motor must be operated alone, so that if a load has been coupled thereto, an operation is required for once disconnecting the load to leave the motor alone, thus incurring a problem of a low efficiency.
Prior Art Example 2 needs complicated software because a single-phase AC current is applied and Fourier series expansion is utilized for the determination of a motor constant, thus requiring a long software processing time, and a large memory capacity for the software.